This invention relates to a crosstalk detecting apparatus for detecting the crosstalk which may arise from an adjacent track and of a recording medium when an image signal that has been FM-modulated and recorded on the recording medium is read out.
A high definition signal having 1,125 horizontal scanning lines per frame requires a much wider frequency band in comparison to an NTSC signal having 525 horizontal scanning lines. Specifically, a frequency band of approximately 30 MHz is needed.
One method of recording such a wide-band high-definition signal on an optical disk or the like is disclosed in Japanese Patent Application No. 2-143589, entitled "Apparatus and Recording Medium for Recording High-Vision Signal".
According to this prior art, three tracks on a recording medium are used simultaneously to accumulatively process an inputted high-definition signal, which is then divided for every three consecutive scanning lines. Signals corresponding to the divided three scanning lines are recorded on the three tracks in a corresponding relationship. In other words, the simultaneous use of the three tracks causes a sweeping time to be multiplied by a factor of three, which in turn, allows the frequency band for the recorded signals to be reduced to 1/3.
When an image signal is recorded on a recording medium, a signal specific having a different level for each of the three tracks (this signal is hereinafter referred to as an identification signal) is added to the image signal in order to identify the three different tracks during reproduction of the signal. The composite signal is then FM-modulated and recorded on the recording medium. Thus, for a period corresponding to the added identification signal a reproduced output contains an FM wave generated when the identification signal was FM-modulated. The FM wave of different frequency is reproduced for each of the three tracks. When using the described three-track arrangement to read out signals from a recording medium on which FM-modulated signals have been recorded, pickups for reading out the signals must be controlled to perpendicularly face the tracks. Generally, for controlling a pickup to face a track correctly, a servo system is employed which detects signals indicative of displacement of the pickup from the perpendicularly facing position of the track, and the moves the pickup so as to reduce the displacement to 0.
The present invention provides an apparatus for detecting a signal corresponding to the above-mentioned signals indicative of a displacement. Conventionally, as described in Japanese Laid-open Utility Model Application No. 59-168835, entitled "Apparatus for Optically Reading Information", light emitted from a light emitting element and reflected by the disk surface is received by a pair of light receiving elements associated with the light emitting element, and the difference between their output signals is output as a displacement.
Conventionally, therefore, the displacement signal is obtained from the difference between output signals from two light receiving elements associated with a light emitting element. For this purpose, the light emitting element and light receiving elements must be placed at highly precise positions, which must be performed by an expert. Also, even if an outputted displacement signal indicates zero, some of the signal read by a pickup may be mixed with crosstalk from an adjacent track.